The present invention relates to medical and diagnostic imaging systems and procedures. Clinical procedures currently employ a number of systems for locating, imaging and diagnosing various structures within the human body. These include x-ray computer tomography, ultrasound, and magnetic resonance imaging, among others. These systems are used to detect morphologic abnormalities associated with specific diseases or conditions in various body organs.
In the case of x-ray computer tomography, for example, a number of projection data are taken sequentially at different angles and the data are used to reconstruct an image of the object being scanned in three dimensions. Thus, an x-ray tomography system solves an inverse problem for the x-ray opacity of body tissues using measurements of the amount of radiation absorbed from many beams transmitted at a variety of angles. This procedure is based on a number of assumptions including that the intensity of the x-rays diminishes across the distance traversed at a rate proportional to the intensity of the beam, that the absorption coefficient depends on the type of tissue along the various beam paths and that this non-linear problem can be solved based upon certain approximations including that a linear set of equations is an accurate representation of the problem. Of critical importance to x-ray tomography is that corrections for scattering are relatively simple.
Others have sought to use the "diffusion approximation" to represent the scattering of optical radiation for medical imaging applications. The diffusion approximation involves the detection of incoherent photons and the analysis of the resulting spectrum. The main problem with this approach is poor spatial resolution which limits the usefulness of this method in medical imaging applications. Others have sought to use so-called "ballistic" photons which travel the shortest path through the medium and are, for the purposes of this application, "non-scattered" photons.
A continuing need exists, however, for further improvements in the field of tomographic imaging for medical applications including enhanced resolution, reduced cost and complexity, and improved diagnostic capability.